Imperium plans to use about $220 million from the offering to construct three new biodiesel plants in Hawaii, Argentina and at an undisclosed location on the East Coast. The company, led by former Loudeye Chief Executive Martin Tobias and former airline pilot John Plaza, plans to open the largest biodiesel plant in the country this summer in Grays Harbor County. It is also evaluating sites in Belgium, China and the Philippines.

The IPO filing was expected. VentureWire reported last month that Imperium was looking to raise between $200 million and $300 million and I reported that the company was looking to have Morgan Stanley take them public.

Imperium plans to trade on the Nasdaq under the ticker “IMPR.” If successful, Imperium’s IPO would be a whopper at $345 million. But it would not be the biggest so far this year. That honor still goes to Kirkland-based Clearwire, which raised $600 million in an IPO in March.

Plaza, who founded Imperium in 2004, would have the most to gain financially in the deal. Through an entity called Odyssey Biofuels, Plaza owns 24 percent of the company. That was followed by Technology Partners, which owns 12.6 percent, and Nth Power, which owns 9.4 percent. Tobias holds 7.7 percent.

UPDATE: My full story on the IPO filing, includes some of the potential pitfalls facing Imperium as well as comments from Craig Cuddeback of the Cleantech Group who notes that the IPO could be an important benchmark for the biodiesel industry.